1. Field of the Invention
The present invention relates to a device for monitoring various variables indicative of molding states of an injection molding machine and a monitoring method.
2. Description of Related Art
In order to monitor molding states or discriminate molding failure, values for various monitoring items for each molding cycle are measured, including molding cycle time, injection time, kneading time, cushion amount, nozzle and barrel temperatures, peak pressure, etc. The measured values are displayed and used for the molding state monitoring and product quality discrimination.
In a known monitoring system (see JP2767654B), for example, measured values of monitoring items acquired for each cycle, such as cycle time, injection time, minimum cushion amount, peak pressure, etc., are displayed in a trend chart form, and their variations are monitored to be utilized for quality control or the like.
In another known system (see JP11-333899A), a change history of set values of molding conditions, such as injection, hold pressure, metering, temperature, etc., is stored and displayed.
In still another system (see JP7-4844B2), values of measured data, such as filling time, plasticization time, injection start time, injection end time, etc., are displayed in the time series for each molding cycle. If set values of various molding conditions change as this is done, the changed items and the set values before and after the change are displayed.
In alternative known systems (see JP2001-293761A and JP2003-1686A), quality data, such as die temperature, filling time, cushion amount, etc., obtained from various sensors are displayed in a data trend graph, a line graph along a time base, or change of molding condition items is discriminately displayed in a colored bar graph. In another system (JP2003-145262A), measured values and set values (reference, upper limit, and lower limit values) for monitoring items are displayed for each shot or molding cycle. In still another system (JP2004-82649A), moreover, set pressure-holding values and their detected values, as well as set speed values and their detected measured values, are displayed for each molding cycle.
As described in JP2767654B and JP2003-145262A and JP2004-82649A, the measured values of the monitoring items indicative of the molding states for each molding cycle are generally obtained and displayed in order to monitor the molding states or discriminate molding failure. Since the measured values of the monitoring items indicative of the molding states vary depending on change of the set values of the correlated molding conditions, moreover, the change of the set values of the molding conditions and the measured values of the monitoring items are displayed together, as described in JP7-4844B2, JP2001-293761A and JP2003-1686A. In the method described in JP7-4844B2, however, monitoring data on the measured values of each shot or molding cycle are displayed in a graphic form, and the set values before and after the change are displayed. Although the time when the set values are changed can be detected with ease, it is hard to grasp the influence of the change on the measured values of the monitoring items.
In the systems described in JP2001-293761A and JP2003-1686A, moreover, the measured values of some monitoring items are displayed as the trend graph along the time base, and sections in which the molding conditions are changed are also displayed. However, the molding condition items with their set values changed and the changed set values are not displayed on the same screen as the trend graph. Thus, it is hard to grasp the influence of the change of the molding conditions on the measured values of the monitoring items.
Since the molding states change depending on the change of the set values of the molding conditions, the apparent measured values of the monitoring items indicative of the molding states change when the molding conditions are changed. However, the molding conditions are diverse and large in number. In general, measured values such as die and barrel temperatures can be supposed to correspond one-to-one to the set values. However, the measured values of the monitoring items never correspond one-to-one to the set values of the molding conditions, and some measured values of the monitoring items change in complicated relation to a plurality of set values.
For example, a generally-called peak pressure or the maximum pressure value that is measured in an injection pressure hold process is an important item in molding quality control. However, the peak pressure changes as the set values of the injection speed, resin melting temperature, injection pressure hold switching position, etc. are changed. Further, the metering time is influenced by a set value of the barrel temperature that melts a resin, as well by set values of the rotational frequency and metering back pressure that are directly related to the action of a metering axis during metering operation. The minimum cushion amount corresponds to the most advanced position of a screw in the injection pressure hold process. It is influenced by set values of very many molding conditions, such as the injection speed, hold pressure, pressure hold time, resin melting temperature, etc., as well as by a metering end position and a switching position for the injection pressure hold process.
As described above, the various monitoring items indicative of the molding states are influenced by the set values of a plurality of molding condition items. In some supposed cases, therefore, the molding condition items that influence the measured values of the monitoring items may vary depending on the set values.